downhiller80 - 2:11 pm on Jan 18, 2010 (gmt 0)

Last year I was working on a site that had a tie-in with another site. When we launched this new promotion, overnight there was suddenly about 8000 links between the two sites. We got blacklisted pretty quickly. I realised our mistake, added rel="nofollow" to the 8000 links, and things were back up and running in a couple of weeks.

So yeah, don't overdo it, and if you have a good user-centric reason for thousands of links, nofollow them!